1. Field of the Invention
This invention reveals an improved apparatus and process for textile spinning, specifically cotton spinning into uniform strong yarns. The disclosed apparatus improves upon electrostatic cotton spinning techniques and in particular improves rotary electrostatic spinning apparatus and processes.
This invention discloses the use of a twisting ground electrode opposite and in conjunction with a rotating conical collecting means having a high voltage twister electrode. The twisting ground electrode helps rotate the yarn tail extending from the twister electrode and electrostatically attaching to the twisting ground electrode.
2. Description of the Prior Art
In the process of becoming yarn, cotton is subjected to carding by which the entangled raw cotton fibers are teased into a more or less parallel alignment. The effect of carding on the cotton is to attenuate a comparatively thick lap of cotton to a gossamer-like film by drawing it out, combing the fibers and then bunching this thin film in a rope form commonly known as a sliver.
Typically the cotton sliver is then further passed through a number of drawing processes which mix the fibers and make them more parallel. In being led through the drawing processes, the sliver becomes drawn out and longer. Generally, to achieve mixing, several slivers are led together through the drawing process so as to yield a single corresponding longer sliver. For fine yarns, the sliver is optionally further combed.
The slivers next are led through special draw-frames and steadily reduced to a thickness of sliver suitable for spinning. Typically, the first of the special draw-frames has four pairs of rollers driven at increasing speeds. In this machine the slivers are mixed or combined and then attenuated by a process known as drafting. The sliver then is typically led through a slubbing frame in which it is drafted by the usual arrangement of pairs of rotating rollers, but on emerging from the last pair of rollers, the sliver is led through a flyer which slightly twists the sliver into an attenuated rope form known as roving and winds this roving onto a bobbin. The roving may then be processed through a roving frame to yield a roving of a degree of fineness and evenness such that it is ready for spinning most types of yarns. (The Standard Handbook of Textiles A. S. Hall, Neywood Books 1969, p. 122-123).
The ring-spinning process used in making yarns for more than one hundred years is based on inserting the spinning twist with the winding operation. The fibers pass from a roving into a spun yarn which is wound on a bobbin in a continuous path. The speed of the overall operation is limited by the mass of the bobbin. This limitation is removed in the more recent open-end spinning processes where the fiber flow is interrupted as it enters the spinning unit. Open-end spinning has a potential for much higher operating rates and for making yarn with fewer knots since bobbins can be larger.
Of the various open-end spinning processes, only rotor spinning has become a serious competitor to ring spinning. Although the rotor spinning machines provide higher production speeds, the yarn generally is not as uniform and is weaker than ring-spun yarn. In view of these factors and the higher cost of the more complex rotor spinning machines, the penetration of the new machines into the textile industry has been relatively small.
In the rotor-spinning process, the fibers are blown into the rotor which is a short open-end cylinder with a tapered inner wall. As the rotor spins, the fibers slip along the inner wall into a collecting groove. The condensed fibers are then twisted and drawn off through an outlet near the center of the rotor. The quality of yarn and the operating speed are limited by the slippage of the yarn in the rotor and the accumulation of trash in the collecting groove.
The best yarns are made with narrow collecting grooves that are especially sensitive to trash accumualtion. Elimination of the collecting grooves is desirable but another method for controlling the fibers is then needed to provide a high quality yarn at high production rates.
Electrostatic forces provide such an alternative to fiber control by narrow collecting grooves. Electrostatic spinning of yarn has been developed as an open-end spinning process. Generally, an electrostatic field is applied between a fiber supply roll and a spinning device. The fibers are charged by induction as they enter the electrical field at the supply roll and are attracted to previous fiber forming a yarn tail and extending from a twister electrode or twisting gripper electrode. Efforts at commercialization of open-end electrostatic spinning have failed to reach competitive or economical production rates. The electrostatic processes have failed because of undesirable reverse twist which produced instability in the free tail of the yarn during twisting by the twister electrode. The reverse twist increases with the spinning speed causing loss of tensile strength and frequent breaks in the yarn at high production speeds.
In the electrostatic spinning process as described by Corbaz, U.S. Pat. No. 3,411,284, roving fibers are charged by induction as they emerge through a pair of rubber and steel delivery rolls. The electrical field is used to align and propel the fibers to the collecting means which is rotated to twist successive fibers into a thread within the collecting means. A tail of the new yarn is formed at the twister or twisting gripper electrode where twist is imparted, and said tail extends to contact the lower portion of the steel delivery roll.
A problem in the prior art has been that, inherently, the end of the long tail extending from the twisting means fails to twist with the yarn in the twister electrode. Therefore, a reverse twist forms in the portion of the tail between the twister electrode and the metal feed roll. Some of the reverse twist eventually is removed as the yarn advances through the twister electrode, but the amount of twist inserted in the formed yarn is reduced, hence yarn strength is reduced. Moreover, visible nodes form in the tail as the yarn attaches and detaches from the metal feed roll and yarn uniformity varies as the tail shifts on the feed roll. Due to these inherent problems, electrostatic spinning has not been widely accepted for high speed commercial spinning.
U.S. Pat. No. 3,768,243 (Brown) described an electrostatic apparatus comprising a stationary electrode element with a tubular projection, a relatively large disc-shaped rotary electrode element and an independently rotating spindle element assembly with a sharp-edged fiber collecting ring. At higher speeds, however, centrifugal effects throw the yarn tail off the fiber collecting ring interrupting the spinning process. Other patents such as U.S. Pat. Nos. 3,696,603 (Kotter) and 4,040,243 (Weller) were attempts to twist the yarn tail and the body of the yarn at the same time using a twisting member which is longer than the basic fiber length, however, both have the drawback that at higher speeds, the fibers sheathing the long twisting member tend to flair from the long twisting and collecting member. The long twisting member does not uniformly release the fibers therefore the fibers come off in surges.
U.S. Pat. No. 4,002,016 (Fischer) described an attempt to use a nonrotatable needle mounted in an electrical insulator to impinge upon the path of travel of fibers being fed to the rotor or twister. Fischer references (column 1, paragraph 3) an unsuccessful apparatus which utilized a rotating fiber brush opposite the rotating yarn end. The Fischer improvement disclosed is an apparatus which includes a nonrotatable needle. The needle is to serve to hold the yarn tail from co-rotating with the twister. At higher speeds in electrostatic processes the Fischer design would give rise to reverse twist forming in the yarn tail causing the yarn tail to attach and detach from the needle therefore forming visible nodes in the finished yarn. Fischer, while recognizing the problem of false twist in mechanical spinning processes (column 2, line 39), does not address the problem of false twist in electrostatic processes. The Fischer nonrotatable needle would enhance the problem of false twist in the yarn tail in electrostatic processes. The present invention obviates the problem of reverse twist in electrostatic processes.